Currently, exhaust gas purifiers that employ a diesel particulate filter (DPF) as a device to remove particulates contained in exhaust gas, such as particulate matter (PM), are put to practical use. During use of such exhaust gas purifiers, particulates such as PM deposit in the DPF, and accordingly, regeneration of the DPF is required. As methods of regenerating the DPF, for example, Japanese Laid-open Patent Publication Nos. 2006-140063, 2003-201825, and 2011-163341 propose methods that employ high-frequency electromagnetic waves such as microwaves. According to such methods, the DPF is exposed to electromagnetic waves such as microwaves to heat and burn particulates such as PM deposited on the DPF, so that the DPF is regenerated. Reference may also be made to Japanese Laid-open Patent Publication No. 2011-252387 for related art.